To me, even correcting some minor but "fixable" abrupt phase rotations and extended group delay spots in the time domain -- of low bass frequencies -- can turn out to be a night and day difference. It's relatively simple enough to A/B test this for onself.
If you are just flattening the phase in-post after minimum phase crossovers have already been applied, there may be no visible difference in the magnitude frequency response at all. However, applying frequency dependent windowing (FDW
) with a low number of cycles might reveal a different story.
While it's true that miniDSP doesn't quite have enough taps available to fix some serious low bass issues, one might be able to nudge the phase just enough to achieve wider coherency across the desired crossover range. Don't get me wrong, I agree that the low number of taps seriously limits the device's capabilities, but I've found myself able to squeeze the heck out of it to gain maximum utility.
miniDSP partial xo phase correction in the left. Additional phase correction via JRiver's convolution engine in right.
See that dip around 80 Hz? It only appears in the graph with frequency dependent windowing applied.
Yeah, the bass looks kind of low below 30 Hz since (in this particular scenario) I was equalizing for the overall room response -- which also maximizes the limited dynamic headroom of my sub & speakers --
i.e. so I can play the drivers as loud as possible without compression or significantly increasing subwoofer bass distortion
.
So the overall room -- call it "power" -- response is nevertheless balanced.
We can see that flattening group delay also increases measurable "
clarity" traces in the bass at our critical xo junction.
And the
wavelet spectrogram looks more linear after fixing that very abrupt (likely room induced) phase rotation / group delay peak:
My EQ strategy here is actually very simple -- a subtractive one -- primarily reducing excess energy in the room:
High pass and low pass filters only for the subwoofer and none applied (or full-range) for the front LR mains.
Crude phase correction curves I came up using rePhase:
Some settings & additional info after generating filters in rePhase
SUBWOOFER Channel
taps: 2036 samples
windowing: hann
sample rate: 96000 Hz
impulse delay: 1018 samples, 10.604 ms
max response: 0 dB, max impulse -0.14 dB
Lt & Rt FRONT MAIN Channels
taps: 1024 samples
windowing: hann
sample rate: 96000 Hz
impulse delay: 511.857 samples, 5.322 ms
max response: 0 dB, max impulse -5.4 dB
JRiver stereo LR (
optional) secondary FIR filter
taps: 12228
windowing: hann
sample rate: 48000 Hz
impulse delay: 6113.999 samples, 127.375 ms
max response: 0 dB, max impulse: -0.09 dB
Here are the raw phase responses using only miniDSP's (2x4 HD)
severly limited filter tap capabilities
Well I say, that's not too bad at all!
Our Sub+Mains Summation Result
No dips created thanks to the largely coherent phase curves.
Lastly (and finally!), the
step response: